Field of the Present Invention
The present invention relates to a substrate handler, a lithographic apparatus and a method for processing a substrate by a substrate handler.
Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In general, the integrated circuit (IC) will comprise a plurality of layers that are provided by sequentially forming different patterns on the substrate. In order to assure proper operation of the IC, it is of utmost importance that the layers that are applied are properly aligned with each other. In this respect, the term overlay is often used to characterize such an alignment. One of the factors that affects the overlay characteristics is the thermal condition of a substrate. In order to obtain a desired overlay characteristic, the sequence of layers forming the IC should be applied to the substrate which the substrate in substantially the same thermal state, which can e.g., be characterized by an absolute temperature of the substrate or a temperature uniformity or a combination thereof.
In order to apply the sequence of layers to the substrate (to form the IC) different processes are performed on the substrate including applying a resist layer, exposing the resist layer, etc.
These processes in general take place in different processing tools such as a lithographic apparatus or a track (e.g., performing a post-exposure bake process and applying a resist layer). As an interface between such tools, a substrate handler or handling tool is in general applied, such tool being provided with one or more ports for transporting substrates to and from the different tools. Often, such a substrate handler is also applied as a buffer for temporarily storing substrates in case the substrates cannot be handled instantaneously by the resp. tools.
Using such a buffering, or in general, handling the substrates by a substrate handler, has been found to affect the thermal condition of substrates when they are received by a lithographic tool for exposure.
As a result, sequentially applied layers of an IC can be provided on a substrate at different thermal conditions (with respect to overall temperature and/or temperature uniformity), thus possibly adversely affecting the overlay characteristics.